Method of spraying thermoplastic paint compositions

ABSTRACT

A coating composition comprising a thermoplastic acrylic polymer in a solution wherein the polymeric solution, devoid of pigment, has a surface tension of less than 25.2 dynes per centimeter at room temperature is particularly useful as an automotive top coating. The coating compositions, when sprayed onto substrates, exhibit increased efficiency of paint deposited per unit of paint sprayed.

United States Patent 1 Porter, Jr. et al.

METHOD OF SPRAYING THERMOPLASTIC PAINT COMPOSITIONS Inventors: SamuelPorter, Jr., Tarentum; Donald P. Hart, Allison Park; Jerome A. Seiner,Pittsburgh, all of Pa.

Assignee: PPG Industries, Inc., Pittsburgh, Pa.

Filed: Feb. 1, 1971 Appl. No.: 111,754

U.S.Cl. ..1l7/75, 117/73, 117/74,

[ 1 Jan. 30, 1973 [56] References Cited UNITED STATES PATENTS 3,194,7777/1965 Christenson et al. ..1 17/132 C X 3,318,714 5/1967 Coney et a1..ll7/132CX 3,429,840 2/1969 Lowe et al ....l17/132 C X 2,849,409 8/1958Evans ....1 17/132 C X 2,949,383 8/1960 Blake ....117/132 C X 3,055,8519/1962 Sanderson ....l17/132 C X 2,934,509 4/1960 Crissey et al...117/75 X Primary ExaminerRalph Husack Attorney-Chisholm and Spencer[57] ABSTRACT A coating composition comprising a thermoplastic acrylicpolymer in a solution wherein the polymeric solution, devoid of pigment,has a surface tension of less than 25.2 dynes per centimeter at roomtempera ture is particularly useful as an automotive top coating. Thecoating compositions, when sprayed onto substrates, exhibit increasedefficiency of paint deposited per unit of paint sprayed.

12 Claims, No Drawings METHOD OF SPRAYING THERMOPLASTIC PAINTCOMPOSITIONS Coatings of thermoplastic acrylic polymers have been usedfor some time now in the automotive industry because of their fineappearance and protective qualities. These coatings, as well as otherindustrial coatings, are generally applied by spraying.

In order to form the thermoplastic acrylic polymer, the acrylic monomersare polymerized in a volatile solvent which is compatable with theacrylic polymer formed (active solvent) so that the coating compositionis in solution ready for use.

The solution of thermoplastic acrylic polymer in active solvent is thenthinned with other solvents or diluents to achieve a consistency properfor spraying.

A major problem of spraying substrates such as automobile bodies andequipment is that up until this time, only a very low coating efficiencywas possible. That is, because of overspray and rebounding of paint offthe substrate, only about half of the paint solids going through thespray gun was actually deposited on the substrate.

Due to the necessity of obtaining good appearance, and a total topcoatfilm build of at least about 2 mils, and the spray gun capabilities, andthe problem outlined above, the prior art has found difficulty inachieving a proper automotive topcoating with less than three coats ofpaint. That is, the entire substrate to be topcoated must be passedthrough the spray unit at least three times. One coat of paint isgenerally defined in terms of production painting as the spraying timebetween two flash periods (periods of evaporation of solvents).

As the three-coat system requires a great dealof time and processexpense, considerable effort has been expended by the paint industrytoobtain a two-coat system whereby the same coating formerly obtained bythree coats could be obtained using only two coats of paint.

It has no been discovered that if a solution of thermoplastic acrylicpolymer in an active solvent wherein the polymer solution devoid ofpigments has a surface tension of less than 25.2 dynes per centimeter atroom temperature is used as the composition at the spray gun, a two-coatsystem will produce a film at least equal in thickness and appearance tothose formed from three-coat systems in the pastplt has beeri'found thatnot only is it possible to obtain a two-coat film build but thatunexpectedly approximately 50 percent less paint is used than used inthe prior art system. With the use of the system of this invention thecosts of coating automotiveand other substrates are reduced enormously,and the hazards or annoyances incidental to'overspray are reduced. 7

The thermoplastic acrylic polymers are generally prepared bypolymerizing the acrylic monomers in an active solvent for the polymerformed or a volatile solvent which is compatable with the polymerformed. Additional solvents or diluents (non-solvents) are then addedtothe solution to thin the composition to a spraying consistency. It iscritical that the composition devoid of pigment at the spray gun have asurface tension of less than 25.2 dynes per centimeter at roomtemperature as it has been discovered that those compositions having asurface tension of greater than 25.2 dynes per centimeter require threecoats for a 2 mil film with good appearance and the efficiency of painttransfer from the spray gun to the substrate will be uneconomical.

The critical surface tension measurement is taken to be that surfacetension measured when the composition is devoid of pigments since theinclusion of pigments has an effect on the surface tension of the paintcom position. Thus, although each color coating containingdifferentpigments may have varying surface tension values, therelationship of surface tension to the efficiency and ability to form atwo-coat build remains the same. Thus, if a coating composition ismeasured at 25.2 dynes per centimeter or lower without the pigments,even though the pigments added will lower the surface tension of thepaint composition, the increased efficiency and film build will beattained.

The thermoplastic acrylic polymer is generally an ester of acrylic ormethacrylic acid or a copolymer of such an ester with anothercopolymerizable monomer. Suitable esters include those of alcoholscontaining about one to sixteen carbon atoms, such as methyl acrylate,methyl methacrylate, ethyl acrylate, butyl acrylate, n-butylmethacrylate, octyl acrylate, lauryl methacrylate, stearyl methacrylate,and 2-ethoxy-ethyl methacrylate. Mixtures of such esters 'may becopolymerized or one or more of the esters may be copolymerized with ahigher alkyl ester or amide of acrylic or methacrylic acid or withanother monomer containing a copolymerizable vinyl group, e.g.,itaconate esters, maleate esters and allyl compounds. The preferableacrylic polymers in this invention are the alkyl methacrylates oracrylates and, more specifically, poly(methyl methacrylate) andcopolymers such as copolymers of methyl methacrylate and butyl acrylate.Blends of the above acrylics with other resins such as epoxys, celluloseacetate butyrate, nitrocellulose and the like may be used. lt ispreferred that the acrylic polymer comprise at least about 40 percent byweight of the blend.

The thermoplastic acrylic polymers are generally formed by polymerizingthe acrylic monomers in an active solvent for the polymerized monomer.An active solvent is one which is volatile and is compatable with thethermoplastic acrylic polymer. These solvents actually dissolve thepolymers.

The active solvents which are useful herein are either aromatichydrocarbons or oxygenated solvents such as esters, ketones, ethers,ether-alcohols, and halogenated hydrocarbons. Examples of these activesolvents are ethoxyethyl acetate (Cellosolve acetate), 2,2,4-trimethyl-l,3-pentanediol monoisobutyrate, acetone,

toluene, methyl ethyl ketone, methyl isobutyl ketone,

disisobutyl ketone, methyl isoamyl ketone, diethyl ether, amyl acetate,butyl acetate, ethylene glycol diacetate, cyclohexanone,trichlorotrifluoroethane, trichloromonofiuoromethane, Z-nitro propaneand the like.

added sufficient additional solvent or diluent (non-solvent) to achieveproper spray viscosity and to achieve the proper surface tension of thepolymer solution.

patible with the acrylic polymers to any appreciable ex- To the polymerand active solvent-must then be tent and are miscible withthe activesolvents. Examples of non-solvents which have been found useful in thisinvention are the liquid aliphatic hydrocarbons-such as hexane, heptane,octane, pentane and VM&P naphtha. Other non-solvents which may be usedare alcohols such as methanol, isopropyl alcohol and the like.

It is noted that mixtures of various active and non-active solvents maybe used herein. It is preferred, in fact, to use mixtures of toluene,acetone and ethoxyethyl acetate as the active solvent portion of thesolution. The preferred non-solvents are hexane and heptane.

It is absolutely necessary that the active and non-active solvents bebalanced so that the polymer is not precipitated and the polymersolution without pigment to be sprayed has a surface tension of lessthan 25.2 dynes per centimeter at room temperature.

The surface of any liquid solution possesses special properties whichare due to the'unbalanced forces of molecular attraction at the surface.The molecules at the surface are pulled inward by the other molecules ofthe liquid and the liquid tends to adjust itself to give the minimumfree energy surface. The surface tension of a liquid (in this case thepolymeric solution) is defined as the forceper centimeter on the surfaceof the liquid whichopposes the expansion of the surface area and isexpressed in dynes per centimeter.

Thus, the surfacev tension is measured by suspending a ring of platinumwire in the body of the liquid and the force requiredto lift the ringfrom the surface of the liquid is measured. (see University Physics,Sears and Zemansky, 2nd edition, Addison-Wesley Publishing Company,Cambridge, Massachusetts (1955) and Physical Chemistry of Surfaces,'ArthurD. Adam'son, 2nd edition, lnterscience Publishers, New York(1967) The means of measuring the surface tension of the polymersolutions ofthisinvention is by the du Nouy method which is a standardASTM-Dl33l method. The measurements are made at room temperature (about72F.) as the fluctuations of temperature will af-' feet the surfacetension of a liquid. The du Nouy apparatus is calibrated by setting theforce at 72 dynes per centimeter for a standard liquid of distilledwater.

3 It has also been found that even more accurate readings may. beobtained when using reagent grade xylene having a surface tension of30.1 dynes per centimeter as an additional standard for calibration.

It is noted that the actual temperature at'the spray unit isapproximately 68F. and the surface tension of the composition will beslightly higher than at room temperature. Y i v 1 The low surfacetension of the polymer solution is generally obtained by balancing thesolvents used. Thus, if a non-solvent having a low surface tension isused such as hexane, enough hexane is used. to lower the surface tensionof the composition to less than 25.2 dynes per centimeter but not enoughto turn the solution from a true solution toa dispersion. It is alsopossible to-balance the properties 'of activesolvents to when balancingsolvents as the. surface tension of a blend may not follow linearly byaveraging the surface tension values of the individual constituents.(See Physical Chemistry of Surfaces, p. 74).

Although the preferred method of achieving lower surface tensioncompositions is by adding liquid. aliphatic hydrocarbon (non-solvents)to the polymer solutions, it is also possible to use only activesolvents wherein the thinner contains enough diethyl ether or otheractive solvent having a low surface tension to lower the surface tensionof the composition to less than 25.2 dynes per centimeter and alsoobtain a twocoat thickness with some increase in paint efficiency.

It may also be desirable to balance solvents having other propertiessuch as certain viscosity levels, evaporation rates, and the like toachieve desired results. It has been found here however, that the mostimportant property which bears upon the possibility of obtainingacceptable automotive two-coat film builds of thermoplastic acrylicpolymer solutions with increased paint efficiency is the low surfacetension of about 4.0 percent by volume of ethylene glycol diacetate,about 21.0 percent by volume of ethoxyethyl acetate and about 9 percentby volume of acetone wherein the paint composition has a surface tensionof about 21.8 dynes per centimeter at room temperature. .Although clearcoatings may be made from unpigmented compositions, it is generallypreferred to add pigments to the paint compositions to be sprayed.Examples of pigments used are titanium dioxide, carbon black, red oxide,phthalo blue, aluminum powder, yellow iron oxide and the like. Ingeneral, any pigment or filler which is, common in the paint, industrymay be added to the coating composition. The critical surface tension.of the composition must still be measured at room temperature withoutthe added pigments.

For automotive coatingsit is also generally desirable to add cellulosicmaterials such as cellulose acetate butyrate or nitrocellulose to theacrylic solutionto improve the metallicorientation' if metallic pigmentsare used. In the preferred embodiment of this invention, celluloseacetate butyrate is' added to the paint composition to be sprayed inamounts of from about 2 to about 30 percent by weight of the paintcomposition.

"Some conventional external plasticizers commonly used for acrylicsolutions are generally added to the paint composition of-thisinvention. Examples of these plasticizers are dibutylphthalate, butylbenzyl phthalate, diisooctyl phthalate, decyl butyl phthalate,diisooctyl adipate, dibutyl sebacate, butyl benzoate, triisooctyltrimellitate, di-n-octyln-decyl trimellitate, tricresyl phosphate,polymeric plasticizers such as polyesters-with or withoutoil-modification and the like; The acrylic solutions generally compriseabout 5 to about 35 percent by weight of the plasticizer.

The paint composition may be sprayed ontoany substrate such as metal,primed metal, wood, plastic, or the like using any conventional sprayingapparatus.

The film build of a thermoplastic topcoating required in the automotiveindustry is generally at least about 2 mils in thickness. Thus, if apolymer solution has a surface tension of less than 25.2 dynes percentimeter the 6 position is sprayed onto both primed and unprimedmetals such as aluminum and steel.

The following examples set forth specific embodiments of the instantinvention. However, the invention substrate will be coated with at leasta 2 mil thickness 5 .is not to be construed as being limited to theseembodiof paint after only 2 passes in the spraying equipment. ments forthere are, of course, numerous possible varia- The conventionalautomotive spray unit is set at a certions and modifications. All partsand percentages in tain fluid feed rate and at these feed rates, theprior art the examples as well as throughout the specification arethermoplastic coating solutions can attain a total film y Welsh! unlessh wi In i ted.

l build on the substrate of only about 0.7 mil per coat. As EXAMPLES theautomftwe reqmremems can for g of A thermoplastic acrylic polymersolution was formed about 2 m1 s, the substrate must be coate t reetimes. by blending 172 parts of a mixture of a percent If attempts solvethe film bluld problem solids solution of a copolymer comprising 90percent craslflg the mud feed rate to achleve the 2 l f 15 methylmethacrylate, and 10 percent butyl acrylate in m only two coats theappearance of the recfumng toluene with 20 parts of cellulose acetatebutyrate and mm unacceptable? to of Sohmon 20 parts of butyl benzylphthalate and forming a 30 perthe Substrate resultmg runmng Palm centsolids solution in a solvent solution comprising 55 Problem cannot beallevated by slmply allowlrfg the parts of toluene '35 parts of acetoneand parts of celspray gun to coat the substrate for a longer period oflosolve acetzna op o l as o mass Produotion of automobiles The abovepigmentless composition was thinned with l a limited time for topooatmgeach mm and the 100 percent by volume of the solvent blends below andProcess Cannot be Slowed down economically and the sprayed onto metalplates using the identical spray gun appearance will also Sufforsettingsfor the same periods of time. All spraying rates Uslng the Process ofthls mvontlon, however, a were based on a delivery rate of 730 ccs ofxylene per coat film build of 2 mils or greater can be achieved at minutthe standard fluid feed rate, spraying each substrate for The followingare the results:

Example Control Percent solvent 1 2 3 4 5 6 7 A B C Toluene 11 11 11 1111 11 Cellosolve acetate.. 25 20 25 25 25 25 Acetone... 27 .t 50

Xylene Ethylene Lactol spir Dlacetone alcohol Hexane 50 Z-propanol2-nitropropanc Cyolohexane. Diethyl ether- 2.8 2.4 1.9 2.2 2.0 2.0 1.61.5 1.1 0. 072 0. 065 0. 061. 0. 061 0. 055 O. 055 O. 012 O. 043 0. 039

l Comprises naphtha and having a specific gravity of 0.735 and a maximumof 20 percent by volume of ethylbcnzene branched ketones,trichloroethylenc or toluene.

the same amount of time. Therefore, a greater efficiency of paint use isachieved than that achieved by the prior art methods. The paintefficiency is measured by spraying a measured volume of paint solids inthe solution at the spray gun and measuring the resulting amount ofpaint deposited on the substrate. Thus the efficiency of thecompositions of the instant invention are compared to prior artsolutions by spraying like amounts of each solution at equal volumesolids at the same feed rates and measuring the film deposition. It hasbeen found that the efficiency of the spray paints of the compositionsof this invention are unexpectedly superior to those of the prior art.Thus, using the method of this invention, substrates such as automotivematerials may be coated with less paint to achieve the same or greaterfilm builds resulting in an appreciable savings.

The coating composition described may be used as a coating for all typesof substrates. Preferably the com- As seen from the above examples thosecoating coinpositions having a surface tension of less than 25.2 dynesper centimeter are markedly superior to the coating compositions havinga surface tension greater than 25.2 dynes per centimeter in both filmbuild and efficiency.

EXAMPLE 8 mixture was put in solution by adding enough of a solventsystem comprising 17 percent toluene, 65 percent acetone, and 18 percentcellosolve acetate to obtain a 30 percent solids solution.

The above solution was pigmented to a metallic blue color by adding 1.5part of aluminum flake and 0.5 part of phthalo blue pigment to 333 partsof the above solution.

The pigmented solution was then thinned for spraying by adding one partby volume of the pigmented solution to one part by volume of a solventsolution comprising 50 percent hexane, 17 percent toluene, 25 percentethoxyethyl acetate, and 8 percent ethylene glycol diacetate. Thesurface tension of the resulting solution was 21.6 dynes per centimeter(21.8 dynes per centimeter clear).

, The unexpected film build and efficiency of the above material whensprayed onto a metal plate was demonstrated by comparing the abovecomposition to the commercial acrylic polymer solution being used in theautomotive industry at the present time which consists of thinning theabove pigmented thermoplastic polymer solution with 100 percent byvolume of a solvent solution comprising 6 percent lactol spirits, 14percent xylene, 31 percent toluene, 14 percent acetone, 18 percentethoxyethyl acetate, percent diacetone alcohol and 7 percent ethyleneglycol diacetate wherein the final solution at the spray gun had asurface tension of 23.5. dynes per centimeter (26.0 dynes per centimeterclear).

The two lacquers were sprayed on an automatic spray machine with exactlythe same setting. The spray units were set to deliver 700 cc of tolueneper minute and the paint compositions were sprayed at that setting. Twocoats of lacquer were applied in both cases. The following illustratesthe results of this test:

Lacquer Thus it is seen that the film build of example 8 is 50 percentbetter than that of the commercial lacquer and that the total amount ofpaintused was approximately the same so that the efficiencywasapproximately 50 percent higher than that of the commercial lacquer.

EXAMPLES 9-12 A thermoplastic acrylic polymer solution was prepared byblending 161 parts of a 36 percent solids solution of a 'copolymer of 90percent methyl methacrylate and 10 percent butyl acrylate in toluene, 26parts of a plasticizer comprising an 85 percent solids solution ofpolymeric polyester comprising 60 percent glyceryl phthalate and 40percent oil having a molecular weight of about 1,200 in xylene and 20parts of cellulose acetate butyrate.

The above polymer blend was reduced with thinner by adding enough of asolvent solution comprising 17 percent toluene, 65 percent acetone, and18 percent cellosolve acetate to obtain a 30 percent solids solution.

The above polymer solutions were pigmented by adding about 1.5 parts ofaluminum flake and about 0.5 part of phthalo blue pigment to 333 partsof the above solution.

The. above pigmented polymer solutions were then.

thinned with percent by volume with the following solvent solutions andsprayed at identical spraying conditions for two coats on a metal panel.The following table shows the results of the film build:

Example Control Spirits Surface Tension (dpnes/cm.) Fi m Build (mils)Thus it is seen that all those examples having a lower surface tensionachieve a superior film build to the control having a greater surfacetension.

EXAMPLE 13 A polymer solution was formed as in example 9. The solutionwas pigmented to a beige color by adding 28.7 parts of TiO,, 1.5 partsof indo yellow pigment, 0.08 part of carbon black and 0.3 part of rediron oxide to 333 parts of the polymer solution.

The above composition was then thinned for spraying by adding 100percent by volume of a solvent solution comprising 50 percent hexane, 17percent toluene, 25 percent cellosolve acetate and 8 percent ethyleneglycol diacetate and two coats were sprayed onto a metal panel. This wascompared to the same composition thinned with 100 percent by volume ofthe commercial thinner of example 8 using the same spray conditions. Thefollowing are the results of the film builds obtained:

, CC of Paint Film Build Example Surface Tension Solids Used. (mils) 1321.4 225 2.5 Control 25.0 200 1.8

EXAMPLES 14-15 Example 14 Control 1 5 I l|l| l Illl 1. It is noted thatother pigmented solutions using the isopropyl alcohol as a diluent showfilm builds similar to that obtained in Example 14 (see Example 7).

EXAMPLE 16 A polymer solution was formed as in example 9.

The polymer solution was pigmented to a white color by adding 45 partsof TiO to 333 parts of the polymer solution.

The pigmented solution was thinned with 100 percent by volume of asolvent comprising 50 percent hexane, 25 percent cellosolve acetate, 17percent toluene and 8 percent ethylene glycol diacetate and sprayed onto a metal panel. This was compared to a thinning of the same pigmentedpolymer solution with 100 percent by volume of the commercial thinner ofexample 1 and spraying under the same conditions. The results are asfollows:

A polymer solution was prepared by blending 24 percent by weight of a 50percent methyl methacrylate polymer blended with 50 percent epoxy resinwith 76 percent by weight of a solvent blend comprising 50.4 percent byvolume of toluene, 32.5 percent by volume of ethyl cellosolve, 13percent by volume of methyl ethyl ketone, 2.0 percent by volume ofacetone, and 2.0 percent by volume of isopropyl alcohol.

The above polymer solution was thinned by adding 37.5 parts by volume ofa solvent solution comprising 48 percent of hexane, 19 percent toluol,15 percent ethylene glycol diacetate and 18 percent cellosolve acetateto 100 parts by volume of the solution.

The above solution was pigmented by adding 12 parts of calcined clay, 10parts of talc, 13.6 parts of TiO 2.5 parts of calcium chromate, and 1.7parts of carbon black to parts of the olymer solids.

he above was compared to t e same polymer solution which was thinnedwith a commercial solvent blend comprising 34 percent toluene, 8 percentacetone, 24 percent cellosolve acetate, 9 percent ethylene glycoldiacetate, 9 percent lactol spirits, and 16 percent xylene to achieve a45 percent by volume reduction and sprayed under the same conditions.

The film builds of both materials after one coating were as follows:

According to the provisions of the patent statutes, there is describedabove the invention and what are now considered to be its bestembodiments. However, within the scope of the appended claims, it is tobe understood that the invention can be practiced otherwise than asspecifically described.

We claim:

1. The method of spraying a paint composition to obtain an increasedefficiency of paint depositing on the substrate after sprayingcomprising spraying onto a substrate a paint composition comprising athermoplastic acrylic polymer in a solvent solution comprising avolatile solvent compatible with the acrylic polymer wherein thepolymeric solution devoid of pigment has a surface tension of less than25.2 dynes per centimeter at room temperature.

2. The method of claim 1 wherein the substrate is primed metal.

3. The method of claim 1 wherein the solvent solution comprises a blendof volatile solvents compatable with the acrylic polymer and a diluentwhich is a nonsolvent for the acrylic polymer.

4. The method of claim 3 wherein the diluent is a liquid aliphatichydrocarbon.

5. The method of claim 1 wherein'the paint composition additionallycontains pigments.

6. The method of claim 1 wherein the paint composition additionallycontains from about 2 to about 30 percent by weight of a solublecellulosic material.

7. The method of claim 6 wherein the cellulosic material is celluloseacetate butyrate.

8. The method of claim 1 wherein the paint composition additionallycontains an external plasticizer.

9. The method of claim 1 wherein the thermoplastic acrylic polymer is ablend of a polymer of alkyl acrylate or methacrylate with an epoxy resinwherein the blend comprises at least 40 percent by weight of the alkylacrylate or methacrylate.

10. The method of claim 1 wherein a volatile solvent compatible with theacrylic polymer is diethyl ether.

11. The method of claim 1 wherein a volatile solvent compatable with theacrylic polymer is toluene.

12. The method of claim 1 wherein a volatile solvent compatable with theacrylic polymer is acetone.

1. The method of spraying a paint composition to obtain an increasedefficiency of paint depositing on the substrate after sprayingcomprising spraying onto a substrate a paint composition comprising athermoplastic acrylic polymer in a solvent solution comprising avolatile solvent compatible with the acrylic polymer wherein thepolymeric solution devoid of pigment has a surface tension of less than25.2 dynes per centimeter at room temperature.
 2. The method of claim 1wherein the substrate is primed metal.
 3. The method of claim 1 whereinthe solvent solution comprises a blend of volatile solvents compatablewith the acrylic polymer and a diluent which is a non-solvent for theacrylic polymer.
 4. The method of claim 3 wherein the diluent is aliquid aliphatic hydrocarbon.
 5. The method of claim 1 wherein the paintcomposition additionally contains pigments.
 6. The method of claim 1wherein the paint coMposition additionally contains from about 2 toabout 30 percent by weight of a soluble cellulosic material.
 7. Themethod of claim 6 wherein the cellulosic material is cellulose acetatebutyrate.
 8. The method of claim 1 wherein the paint compositionadditionally contains an external plasticizer.
 9. The method of claim 1wherein the thermoplastic acrylic polymer is a blend of a polymer ofalkyl acrylate or methacrylate with an epoxy resin wherein the blendcomprises at least 40 percent by weight of the alkyl acrylate ormethacrylate.
 10. The method of claim 1 wherein a volatile solventcompatible with the acrylic polymer is diethyl ether.
 11. The method ofclaim 1 wherein a volatile solvent compatable with the acrylic polymeris toluene.